The sparkling translucent stone was sold to a phone bidder at the Sotheby's auction for Hong Kong dollars 238.68 million (USD 30.6 million) following bidding that lasted for more than six minutes.
The egg-shaped stone has been described as the finest of its kind ever to appear at auction. Earlier estimates valued it at USD 28-USD 35 million.
The stone, dubbed the "Magnificent Oval Diamond", was discovered in a deep mine in an undisclosed southern African country in 2011.
The stone, described by Sotheby's as "the largest D colour flawless diamond", has been given the highest quality rating awarded by the Gemological Institute of America.
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"D colour" diamonds are rare and colourless and fetch premium prices.
The sale beat the record set at a diamond auction last year, when a 101.73-carat diamond was sold for USD 26.7 million.
Hong Kong has become a centre for jewellery auctions thanks to growing wealth in China and other parts of the region.